There is a known mobile wireless communication system, which increases a reception gain using a plurality of antennas to improve the reception performance at a base station or a mobile terminal.
Here, there is a fading as one of factors which cause deterioration of the reception performance. The fading is a phenomenon in which radio signals transmitted from a base station or a mobile terminal arrive through lots of paths due to reflection, refraction and scattering by buildings, vehicles, trees and the like existent between base stations and are rendered to be multipath signals. When such multipath fading occurs, the received power fluctuates at a reception antenna end. Thus, a plurality of antennas is prepared at the reception side to increase the received power, and thereby the influence by multipath fading is reduced.
FIG. 9 is a functional block diagram illustrating a schematic configuration of a main part of a conventional wireless communication apparatus reducing the influence by such multipath fading to increase a reception gain. The wireless communication apparatus is provided with a plurality of antennas 101-1 to 101-M. Arrival signals received by the antennas 101-1 to 101-M are reception-processed and A/D-converted by the corresponding reception units 102-1 to 102-M. Output signals from these reception units 102-1 to 102-M are diversity-combined by a combining circuit 103 so that combined received power is maximum, and thereafter the combined reception signal is equalized by an equalizer 104 and then error-corrected and decoded by a decode circuit 105.
Here, there is known, as an example of methods for combining a plurality of reception signals at the combining circuit 103, a method in which a known information signal inserted in a reception signal is used to calculate, for each antenna, an antenna weight at which the phase error of the received known information signal is a minimum using MMSE (Minimum Mean Square Error), and based on the calculated antenna weights, phase of reception signals from reception units are corrected and the reception signals are combined to obtain a combined reception signal having a sufficiently high SNR (Signal to Noise Ratio) (see Patent Document 1, for example).
In the conventional wireless communication apparatus shown in FIG. 9, the combining circuit 103 performs, prior to combining reception signals from reception units, first equalization for correcting the phase of each reception signal, and then the equalizer 104 performs second equalization on the combined reception signal based on the amplitude of the known information signal. Moreover, the decode circuit 105 performs, using reliability information (combined power) generated in the second equalization of the combined reception signal by the equalizer 104, error correction on the combined reception signal and decodes it, and then outputs the result. The error correction method using such reliability information is disclosed in Patent Document 2, for example.
Moreover, there is also known, as another method for combining signals received by a plurality of antennas, the MRC (Maximum Ratio Combining) in which phases of signals received by antennas are corrected using a known information signal inserted in the reception signals, and the reception signals are weighted and combined according to levels of the respective phase-corrected reception signals so that the combined received power becomes large.    Patent Document 1: JP 2003-501971 T    Patent Document 2: WO 2004/082182